1. Field of the Invention
The present invention relates to a system for identifying a position of a tire provided in a vehicle.
2. Description of Related Art
In recent years, regulations with regard to vehicle safety have been enhanced both in Japan and United States. According to the TREAD (Transportation Recall Enhancement Accountability and Document) act, new automobile to be marketed in North America in future will be required to be equipped with a TPMS (tire pressure monitoring system). Such a system (TPMS) is effective in improving automobile safety. Therefore, it is recommended that automobile marketed outside North America be equipped with this system.
FIG. 1 is a block diagram showing a TPMS disclosed in Japanese Laid Open patent Application (JP-A-Heisei8-227492). Referring to FIG. 1, the TPMS 100 is provided with a sensor 1 for each wheel of a vehicle, a detection unit 2 for each sensor 1 and a monitor unit 103. The detection unit 2 is placed in the body section of the vehicle to face toward the sensor 1. A driver in the vehicle can watch the monitor unit 103. The sensor 1 detects air pressure of a tire mounted on the wheel. A detection result acquisition section 121 of the detection unit 102 acquires the detection result from the sensor 1. A data generator section 122 of the detection unit 102 converts the detection result into a digital data and provides the digital data with an ID (identification) code assigned to the detection unit 102. A transmitter section 123 of the detection unit 102 transmits the digital data with the ID code as radio wave signal, A receiver section 131 of the monitor unit 103 receives the radio wave signal. A CPU 132 of the monitor unit 103 makes a display section 133 to display the detection result. When the detection result indicates a warning condition of the tire, the CPU 132 makes an alarm section 134 to raise the alarm.
The sensor 101 is provided in the tire mounted on each wheel. Therefor, air pressures of all tires of the vehicle can be monitored individually and accurately.
When the tire condition is monitored by using the TPMS described above, it is required to identify positions of tires in a vehicle. Japanese Laid Open patent Applications (JP-P2004-224160A) and (JP-P2005-147709A) disclose arts to identify positions of tires.
FIG. 2 is a block diagram showing a TPMS disclosed in Japanese Laid Open patent Application (JP-P2004-224160A). Referring to FIG. 2, the TPMS includes sensors 215 to 218, receiver sections 211 to 214, a controller 205, a display 206 and an alarm lamp 207. The sensors 215 to 218 are provided respectively to tires 201 to 204 of a vehicle 200. The receiver sections 211 to 214 are provided in a main body 210 of the vehicle 200. The receiver sections 211 to 214 are provided respectively in vicinities of the tires 201 to 204. Each of the sensors 215 to 218 detects air pressure of the corresponding tire and transmits through air a signal indicating the air pressure and an identification code assigned to that tire. The receiver sections 211 to 214 receive the signal and provide the air pressure data and the identification code to the controller 205. Here, the signal transmitted from the sensor 211 is received by each of the receiver sections 211 to 214. The tire 201 with which the signal is concerned is identified as a tire in the vicinity of the receiver section 211 by comparing intensity of the signal received by each of the receiver sections 211 to 214.
FIG. 3 shows a flow chart of a method for identifying tire position disclosed in Japanese Laid Open patent Application (JP-P2005-147709A). In a system concerned with the method, sensor units are respectively provided to wheels of a vehicle. Each of sensor units includes an acceleration sensor and transmits through air a signal indicating a time (called as detected time) required for one rotation of the corresponding wheel, an identifier and an air pressure of a tire mounted on the corresponding wheel. A receiver receives the signal from each of the sensor units and sends data corresponding to the signal to the controller. The receiver is installed in the front region of the vehicle. The controller judges whether each of the sensor units is provided to the front wheel or the rear wheel of the vehicle based on the intensity of the signal. Referring to FIG. 3, in steps S1 and S2, a controller compares a steering angle of the vehicle with a predetermined value at every reception of the signal from the sensor unit. In step S3, when the steering angle is larger than the predetermined value, the controller calculates a time (called as calculated time) required for one rotation of the wheel based on speed of the vehicle and size of the tire. In step S4 and S5, the controller compares the calculated time with the detected time. In step S6, when the calculated time is longer than the sum of the detected time and a predetermined time, the controller judges the sensor unit as a sensor unit provided to the outside wheel. In step S7, when the calculated time is shorter than the difference calculated by subtracting the predetermined time from the detected time, the controller judges the sensor unit as a sensor unit provided to the inside wheel. In step S8, the controller judges whether the outside (inside) wheel is the left wheel or right wheel based on the direction of turn of the vehicle.
The present inventor has recognized that according to the TPMS disclosed in Japanese Laid Open patent Application (JP-A-Heisei8-227492), it is difficult to identify automatically the positions of tires. Because not specified is a correspondence between the position of the detection unit and the ID code.
The present inventor has also recognized that according to the TPMS disclosed in Japanese Laid Open patent Application (JP-P2004-224160A), the same number of the receiver sections as the number of the wheels are required. The plurality of receiver sections increases the number of parts required for manufacturing the vehicle with the TPMS. Moreover, lines are also required for connecting the receiver sections with the controller. These factors may increase the manufacturing cost for the vehicle.
The present inventor has also recognized that according to the method disclosed in Japanese Laid Open patent Application (JP-P2005-147709A), the position of the tire can be identified only during the turn of the vehicle. The place in which the receiver should be installed is restricted in order to judge whether each of the sensor units is provided to the front wheel or the rear wheel of the vehicle based on the intensity of the signal. Moreover, the controller requires data indicating whether the receiver is installed in the front region or rear region of the vehicle.